Boilers are a key component of coal-fired power plants and all kraft pulp mills, being the production bottleneck in most such mills. For financial reasons, it is therefore critical to avoid unscheduled boiler outages and to maximize the run times of these boilers. In order to prevent forced outages due to plugging of the convective passages around boiler tubes, sootblowers are used to remove saltcake deposits from the boiler tubes, but as currently employed, sootblowers are often not very effective and the current use of sootblowing steam is inefficient. Sootblowers are often operated on a fixed schedule with little or no feedback based on the actual degree of fouling in any given region of the convective section. Currently the principal means for collecting direct information on the degree of fouling is through the use of infrared inspection cameras such as those currently marketed to the pulp and paper, cement, and power generation industries. While these systems provide relatively clear images of the front of the superheater and in the sootblower lanes in the generator section, their ability to provide images at the back of the generator bank, in the economizer, and in the precipitator) or to provide images of deposits in the gas passages between tube banks is severely limited. Imaging in the economizer is limited by the relatively low temperatures and correspondingly low levels of thermal radiation, low contrast in that part of the boiler, and by the limited sensitivity of current infrared imaging sensors.
The limitation on imaging in the gas passages is the result of the geometry of the boiler and the fact that deposits in these regions cannot be seen from the inspection ports located on the side walls of the boiler. It is possible, with a suitable periscopic lens system that can be inserted into the boiler, to obtain images of deposits in the gas passages between tube banks. However, this periscopic lens tube is extremely expensive and suffers from relatively poor optical quality. Therefore, there is a need for an imaging system that can produce clear images of deposit formation throughout the interior of the process equipment such as a boiler—even in areas of low temperature such as the economizer or precipitator. There is also a need for an imaging system capable of producing images in areas that are currently inaccessible due to geometric constraints imposed by the construction of the boiler.
Another key unmet need is to be able to quantitatively measure the thickness of deposits on boiler tubes and other internal surfaces of the process equipment to enable the operator to assess the degree of fouling of these interior surfaces, such as convective pass tubing. Deposits on such tubes impede heat transfer and, if left unchecked, can eventually block the gas passages between the tubes causing a forced outage which, as discussed above, can be extremely costly. A much better approach would be to quantitatively measure the thickness of deposits on boiler tubes. This capability would provide real-time information on deposit buildup and sootbiower effectiveness and would facilitate implementation of feedback-controlled sootblowing allowing substantial reductions in sootblowing steam usage.